The present invention relates to reservoirs with hydrogen storage material for selectively storing and discharging hydrogen.
Like solar energy, hydrogen energy is now widely known as clean energy. However, to actually produce energy with hydrogen, easy storage and transportation of the substance is indispensable. Hydrogen storage material (hereinafter referred to as “HM”), which is, for example, an alloy, is considered as a solution to this problem. HM absorbs hydrogen to become a hydride at a certain pressure and at a certain temperature and releases hydrogen at a different pressure and at a different temperature. H/M is used as a hydrogen supply in hydrogen engines and fuel cells, which are now under development. Likewise, heat pumps that use H/M are now being developed. More specifically, the heat pumps use exothermic reaction and endothermic reaction caused by HM. The exothermic reaction takes place when H/M absorbs hydrogen, and the endothermic reaction takes place when HM releases hydrogen.
It is thus preferred that a reservoir with hydrogen storage material (hereinafter referred to as “HM reservoir”) includes a heat exchanger. The heat exchanger allows HM to operate smoothly. Japanese Unexamined Patent Publication No. 6-193996 describes an HM reservoir shown in FIG. 8. The HM reservoir includes an outer housing 50 and an inner housing 51. The inner housing 51 accommodates a heat exchanger 54. The heat exchanger 54 includes a heat pipe 52 and a plurality of fins 53, which are aligned along the heat pipe 52. Each space between adjacent fins 53 is filled with NM powder (not shown). Hydrogen gas is supplied to the interior of the inner housing 51 through a hydrogen pipe 55. The gas is discharged to the exterior of the inner housing 51 through the hydrogen pipe 55.
As described, the heat exchanger 54 of this HM reservoir includes the fins 53. The structure of the HM reservoir is thus complicated, and the HM reservoir is not easy to assemble. Also, it is complicated and time consuming to fill HM powder in each space between adjacent fins 53 with uniform density. If the density is varied among different spaces, hydrogen is not smoothly released by HM powder in a space in which the density is relatively high. Further, when HM expands during hydrogen absorption, reactive force acts on the fins 53 non-uniformly due to the HM powder's density variation. This shortens life of the HM reservoir.
FIG. 9 shows an HM reservoir described in Japanese Unexamined Patent Publication No. 9-142801. The HM reservoir includes a container 56 that accommodates a plurality of HM molded bodies 57. An HM molded body 57 is formed by compressing a mixture of HM powder and binding material (fluorine contained resin). A hydrogen-gas-permeable sheet 58 is provided between adjacent HM molded bodies 57. Each sheet 58 forms a hydrogen gas passage. The sheet 58 corresponds to a hydrogen gas port 59 that extends through the container 56.
The HM reservoir of FIG. 9 that employs the HM molded bodies 57 solves the problem caused by the HM reservoir of FIG. 8, which uses HM powder. However, the publication corresponding to FIG. 9 does not specify a method for cooling the HM molded bodies 57 during hydrogen absorption or a method for heating the HM molded bodies 57 during hydrogen release.
Since exothermic reaction takes place when HM absorbs hydrogen, the material need be appropriately cooled to smoothly absorb hydrogen. In contrast, since endothermic reaction takes place when HM releases hydrogen, the material need be appropriately heated to smoothly release hydrogen. Accordingly, it is necessary to optimize a method for selectively heating and cooling HM to allow the material to operate smoothly. However, the HM reservoir of FIG. 9 does not include an internal mechanism for selectively heating and cooling HM, which should otherwise be incorporated in the container 56. It is thus necessary to provide an external means for selectively heating and cooling the container 56. In this case, heating and cooling of HM is not efficiently performed, and HM's hydrogen storage rate is reduced.
Particularly, if the HM reservoir is installed in a vehicle driven by a hydrogen engine or a fuel cell, it is necessary to minimize the reservoir while maximizing the amount of hydrogen stored in the reservoir. Accordingly, HM's hydrogen storage rate must be improved.